Upon insertion into the lumen of the endoplasmic reticulum (ER), many newly synthesized proteins are modified by addition of oligosaccharide side chains to asparagine residues (N-linked sugar chains). Processing of N-linked sugar chains is initiated within the ER by sequential removal of glucose residues by glucosidase I and glucosidase II enzymes, a process referred to as glucose trimming. A growing body of evidence signifies that glucose trimming is important for association of many nascent glycoproteins with calnexin, a molecular chaperon that functions in the assembly/folding of oligomeric protein complexes. Indeed, calnexin association is believed to be an important step in the assembly of several major immune receptor proteins, including major histocompatibility complex (MHC) class I and class II molecules and the antigen receptors expressed on T and B lymphocytes. We studied the role of glucose trimming and calnexin association in the assembly of MHC class I proteins and T cell antigen receptor (TCR) proteins.